The present disclosure relates to a vehicle antifogging system.
Generally, dew condensation occurs on a surface of a window mounted to a vehicle when it rains or snows or in other situations. Such dew condensation, i.e., formation of water droplets on the window surface by moisture in the atmosphere, is caused when the temperature of one of the surfaces of the window becomes lower than the dew point due to the atmospheric temperature and humidity inside and outside the window, or when the window is subjected to a sudden change in temperature. The dew condensation causes scattering of light transmitted through the window, and consequently causes fog. Fog occurring on the window obstructs the driver's field of view, and may impede the driving.
When fog occurs on the window due to dew condensation, a defroster vaporizes the water adhering to the internal surface of the window to defog the window. For example, the defroster is configured to defog the window by sending, from an air outlet of the defroster, conditioning airflow to the internal surface of the window while sucking outdoor air having a low humidity, as a compressor of an air conditioning unit is driven by a power source and an evaporator functions as a dehumidifier.
As can be seen, since ventilation takes place when the defroster operates to defog the window, the temperature in the vehicle cabin decreases, in particular, in cold weather. In such a situation, a thermal load is required to return the vehicle cabin temperature after the ventilation to an appropriate temperature.
Meanwhile, in recent years, it has been required to reduce the thermal load for maintaining the temperature in the vehicle cabin at an appropriate temperature, in view of the need of, for example, regulation of carbon dioxide emission and improvement of fuel economy. As discussed above, the load of ventilation (specifically, the ventilation taking place when outdoor air is sucked to operate the defroster) to defog the window constitutes a large percentage of the thermal load in cold weather. Reducing the operation of the defroster causing the ventilation load enables effective reduction in thermal load, and is expected to improve the fuel economy.
For this reason, to reduce the operation frequency and/or the operation time of the defroster, a technique for making a vehicle window resistant to fogging is proposed: it is proposed to provide a window with antifogging treatment, i.e. formation of a special coating on the window. Specifically, an exemplary window provided with such antifogging treatment has, on its surface, a hydrophilic, water-slipping or water-absorptive coating, and is resistant to dew condensation that causes fog. Thus, use of this antifogging means causing no thermal load leads to reduction of the ventilation load.
In the case of using a hydrophilic coating, water adhering to a surface of the coating forms a film, reducing the formation of water droplets. In the case of using a water-slipping coating, water droplets on a surface of the coating slip down along the coating. In the case of using a water-absorptive coating, water adhering to the surface of the coating is absorbed into the coating, reducing the formation of water droplets.
Using these antifogging coatings reduces scattering of light caused by water droplets on the window, and accordingly, can reduce the operation opportunities and/or the operation time of the defroster.
Among the antifogging coatings described above, the water-absorptive coating has received attention because it advantageously makes it difficult for water droplets to remain on the surface, and for the absorbed water to freeze in the coating.
In the case of using the water-absorptive coating, when the quantity of water absorbed in the coating reaches the largest possible quantity that can be absorbed in the coating (hereinafter referred to as the “saturated water absorption volume”), the coating no longer can absorb water, and water droplets form on the surface of the coating.
With respect to this problem, for example, Japanese Patent No. 4670418 discloses a technique of detecting a quantity of water contained in a coating, and operating a defroster when the quantity of water reaches a predetermined quantity, so as to vaporize the water in the coating. This technique enables recovery of the water absorptive capacity of the coating by operating the defroster according to the quantity of water in the coating.